A comprehensive study on the structure and function of the renal lymphatic system is in progress and renewal funds are requested to proceed with the work. The substantial progress already made on mapping the pattern and distribution of intrarenal lymphatics will be extended to develop a three dimensional portrayal of the system, from reconstruction diagrams of serial light and electron micrographs. Quantitative data will be derived on the extent of the lymphatic network, and on the specific relationships which the network has to the various elements of the nephron and the intrarenal vasculature. The specialized techniques which have been developed to display the lymphatics of the cortex will be applied to the renal medulla in order to determine whether or not medullary lymphatics exist. If present, a qualitative and quantitative analysis of their extent and distribution will be obtained. The morphologic aspect of the proposal also encompasses a cortical and medullary study of the passage of tracers through capillary wall, interstitium and lymphatic capillary endothelium. If medullary lymphatics do not exist, then interstitial pathways taken by macromolecules become of special importance. Functional studies, involving collection and analysis of hilar and capsular lymph, thoracic duct lymph, and arterial and renal venous plasma will be directed at specific questions on the sources of renal lymph. These questions have arisen from our work to date. The work will be extended to measure plasma and lymph renin activity under different conditions of renal function in order to determine whether lymph, with its high content of renin and its morphological relationship to the juxta-glomerular complex, can be used as a highly sensitive monitor of renin secretory activity and release.